Emmanuel Macron's France has threatened to block the port of Calais to the UK under a No Deal Brexit

As the nation’s only major roll-on roll-off ferry hub, the Dover-Calais crossing has been identified by DexEU officials as Britain major strategic weak point.

France has the power to spark huge delays for UK-bound lorries importing factory parts for ‘just in time’ supply chains such as car factories.

And French customs officials would draw a halt to a large chunk of Britain’s food exports from entering France.

Brussels has the power to refuse to grant the UK approval to export animal products such as meat, poultry and dairy to the EU - trade worth £3.5bn a year - as well as organic food for as long as SIX months.

If Theresa May refuses to pay the UK’s £39bn divorce bill, France could wreak havoc with cross-channel trade, the Cabinet was warned

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Theresa May’s top table was told that the drastic moves would see British factories forced to be mothballed, and leave food produce rotting – driving smaller firms and some farmers out of business within a few weeks.

In his own presentation to an earlier Cabinet meeting, Mr Javid also revealed that French border guards could cause hours of tailbacks by simply insisting on asking drivers for their reason for travel.

The Dover-Calais crossing has been identified by DexEU officials as Britain major strategic weak point

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“There is simply no alternative to Dover for just-in-time manufacturers or food exporters, and they together support a significant number of jobs.

“It would do northern French a lot of damage too, and really decimate Ireland, but we expect President Macron will initially attempt some heavy disruption in Calais to turn the screw on us to pay up.”

Transport Secretary Chris Grayling said this week that alternatives to Calais such as Harwich and Felixstowe could replace Calais if France is difficult.

But another Cabinet source hit back to say no other British port in the south east is either deep enough or has the surrounding infrastructure to handle the size of Dover’s trade.

The source added: “Grayling is talking b******s, he literally doesn’t know what he’s talking about. There is no workaround to Dover, and rail or air freight is offers nowhere near the same capacity either”.

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The Financial Time also reported last night that the Cabinet was briefed yesterday on plans to charter ships to bring in emergency food and medicines to other ports under a no-deal Brexit if Calais get clogged up.

But Mrs May told the meeting: “The government’s priority is to secure a deal”.